1. The airtightness of the sampling line of the analyzer
The supporting pipeline of the trace oxygen analyzer should be sealed. A very small leak will cause the oxygen in the ambient air to diffuse in, resulting in a high measurement value.
Although in the measurement, the sample gas pressure is greater than the ambient pressure, but the oxygen in the sample gas is a micro-scale. According to Ferrari's law, the partial pressure of oxygen is proportional to its volume content. The atmosphere contains about 21% oxygen, and PPM. The oxygen partial pressure of the sample gas of the calculated concentration differs by about 10,000 times, so the partial pressure of the trace oxygen in the gas sample is much lower than the partial pressure of oxygen in the atmosphere. When the leak occurs, the oxygen in the atmosphere will rapidly spread from the leaking part. Come in.
Secondly, the sampling pipeline should be as short as possible, the joints should be as small as possible, and the joints and valves should be sealed well. After the pipeline is connected, the air tightness inspection should be done.
Request for air tightness test: Under 0.25 MPAm test pressure, the pressure drop is not more than 0.01 MPA for 30 minutes.
2, the selection of sampling material for the trace oxygen analyzer
The pipeline material is basically made of copper or stainless steel pipeline, and the secondary PTFE tube is selected. Forbidden selection of pipes such as latex tubes and white rubber tubes, the air tightness and material resistance to penetration are too poor, and the measurement of trace oxygen is too much error under the standard measurement pressure. The outer diameter of the pipeline is usually 6mm or 1/4IN. We also choose 3mm or 1/8IN. In short, choose stainless steel tube, clean and degrease, and keep the inner wall of the tube clean. For the analysis of trace level (<1PPMV) oxygen, The inner wall polished stainless steel tube should be selected. The selected valve and joint should have a dead volume as small as possible.
3, the time of sampling and analysis of the elements of temperature
In order to prevent the moisture in the sample from condensing and condensing on the tube wall, forming a dissolution and absorption of trace oxygen, the sampling pipeline should be insulated or heat-insulated according to the condition. When detecting trace oxygen in liquid nitrogen, special attention should be paid to heating measures. Otherwise, since the boiling point of oxygen is lower than the boiling point of nitrogen by 13 degrees, the sample gas is not vaporized evenly, which will make the measured value seriously lower.
4. The closer the sampling point is to the analyzer, the better.
The measurement position of the trace oxygen analyzer should be as close as possible to the measurement point, so as to avoid excessive pipelines and excessive unreliable factors, which affect the reliability of the measurement data.
5, the sample gas sampling process should be clean and clean
The sample gas should not contain oil components or solid particles to avoid clogging and contamination of the membrane.
6, the sample gas can not contain corrosive gases
The sample gas should not contain sulfide, phosphide or acid gas components. These components pose a hazard to fuel cells, particularly alkaline fuel cells.
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